4,4&#39;-Thio-bis-(dialkylphenol)/formaldehyde condensates and process for producing them

ABSTRACT

A phenol/formaldehyde condensation product of a 4,4&#39;-thio-bis-(dialkylphenol) and formaldehyde having a molecular weight of 1,000 to 4,000; a process for preparing such a condensation product by contacting 4,4&#39;-thio-bis-(dialkylphenol) and a source of formaldehyde in the presence of a protonic acid catalyst; and the use of such a condensation product as an antioxidant in an olefin polymer or copolymer composition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the preparation of bis-phenoltype/formaldehyde condensation products and especially a4,4'-thio-bis-(dialkylphenol)/formaldehyde condensation products havinga molecular weight of between 1,000 and 4,000 and the use of thecondensation product as an antioxidant in olefin polymeric orcopolymeric compositions. This invention is particularly directed to thecondensation products themselves.

2. Discussion of the Prior Art

It is known that phenol and its partially substituted derivatives reactwith carbonyl compounds to form higher molecular weight condensationproducts having non-uniform structure. However, under specific reactionconditions or with particular carbonyl compounds, there are alsoobtained low molecular weight condensation products. It has becomedesirable to provide higher molecular weight products obtained by thecondensation of formaldehyde or a source of formaldehyde and asubstituted phenolic compound. More especially it has become desirableto provide such a condensation product which is compatible with olefinpolymeric or copolymeric compositions to impart to such compositionsantioxidant properties.

Accordingly, it is an object of the present invention to provide aprocess for the production of alkyl-substitutedbis-phenolic/formaldehyde condensates having higher molecular weights,say, in the region of 1,000 to 4,000 which are compatible with olefinicpolymers or copolymers so as to function in such compositions asantioxidants, albeit present in small quantities.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a4,4'-thio-bis-(dialkylphenol)/formaldehyde condensation product,especially a condensation product having a molecular weight of 1,000 to4,000. In accordance with this invention there is also provided aprocess for the production of such a condensation product having amolecular weight of 1,000 to 4,000 which process comprises contacting a4,4'-thio-bis-(dialkylphenol) having a free hydrogen atom in an orthoposition with respect to each phenolic hydroxyl group with formaldehydein the presence of a protonic acid, as catalyst. Generally speaking, theprocess can be conducted, if desired, in the presence of a solventalthough a solvent is not required. The mole ratio of the4,4'-thio-bis-(dialkylphenol) to formaldehyde was generally in the rangeof 1:0.5 to 10 and the mole ratio of the 4,4'-thio-bis-(dialkylphenol)to protonic acid catalyst is in the range of 1:0.01 to 10.

In accordance with this invention there is provided aphenol/formaldehyde condensation product having a repeating unit of theformula ##STR1## or one having a repeating unit of the formula ##STR2##wherein n is 3 to 12 R₁ and R'₁ are each independently selected from thegroup consisting of straight chained alkyl of 1-8 carbon atoms, branchedchained alkyl of 1-8 carbon atoms, R₂ and R'₂ are each independentlyhydrogen, straight chained alkyl of 1-8 carbon atoms and branchedchained alkyl of 1-8 carbon atoms. Generally speaking, the molecularweight of the condensation product is between 1,000 and 4,000,preferably between 1000 and 2000, the molecular weight being determinedby vapor pressure osmometer and K. Rast-Method.

Generally speaking, the 4,4'-thio-bis-(dialkylphenol)/formaldehydecondensation products are obtained by employing a4,4'-thio-bis-(dialkylphenol) which has the general formula ##STR3##wherein R₁ and R'₁ are straight chained alkyl groups of 1-8 carbon atomsor branched chained alkyl groups of 1-8 carbon atoms or branched chainedalkyl groups of 1-8 carbon atoms and R₂ and R'₂ are hydrogen,straight-chained alkyl groups of 1-8 carbon atoms or branched chainedalkyl groups having 1-8 carbon atoms. Examples of these compoundsinclude 4,4'-thio-bis-(3-methyl-6-t-butylphenol),4,4'-thio-bis-(3-isopropyl-6-t-butylphenol),4,4'-thio-bis-(3,6-di-t-butylphenol),4,4'-thio-bis-(3-methyl-6-isopropylphenol),4,4'-thio-bis-(3-propyl-6-t-butylphenol),4,4'-thio-bis-(3-isopropyl-6-isoamyl-phenol) and4,4'-thio-bis-(6-t-butyl-phenol). Thus, in the preferred embodiment ofthe present invention R₁ and R'₁ are branched chained alkyl groupshaving up to 8 carbon atoms, especially having 1-4 carbon atoms.However, it is also possible to employ asymmetric bisphenols in theprocess of the invention.

In the process of the present invention a bisphenol having a freehydrogen atom in the ortho position with respect to each phenolichydroxy group is employed. It is believed that it is this hydrogen whichinfluences the reactivity of the hydroxyl group and thus allows for thepreparation of polymers having either or both of the structural unitsdepicted above.

In conducting the process a source of formaldehyde is employed. Whilethe source of formaldehyde is in many instances preferably an aqueoussolution of formaldehyde such as one containing 30 to 40% by weightHCHO, e.g., a formalin solution, any monomeric or polymeric source offormaldehyde is suitable. Thus the process can be conducted employingparaformaldehyde as a formaldehyde source.

Various inorganic or organic protonic acids can be used as catalysts forthe bisphenol-formaldehyde reaction. Preferably, the protonic acidcatalyst is one from the group consisting of hydrochloric acid,phosphoric acid, p-toluene sulfonic acid and mixtures of hydrochloricacid with oxalic acid, sulfuric acid or boric acid. The use of mixturescontaining oxalic acid has been found to be particularly useful owing tothe reducing properties of the oxalic acid which provide condensationproducts having a particularly bright and desirable color. The moleratio of the 4,4'-thio-bis-(dialkylphenol) to protonic acid is generallyin the range of 1:0.01 to 10, preferably 1:0.1 to 1.

It is considered particularly surprising that high molecular weightmaterials of the order of 1,000 to 4,000 are provided by the use of4,4'-thio-bis-(dialkylphenol) inasmuch as the reactant, especially whenone of the alkyl groups is a tertiary or branched alkyl group, isstearically hindered due to the presence of the alkyl groups adjacentthe phenol hydroxy groups. A reduction in their reactivity would havebeen expected.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The reaction of formaldehyde with the sulfur-containing bisphenols whichis carried out especially with molar ratios of 1:0.8 to 1:3.0 can beeffected in an extremely simple manner. Depending upon the selectedreaction parameters, i.e., the amount of protonic acid charged and/orthe ratio of 4,4'-thio-bis-(dialkylphenol) to formaldehyde, themolecular weight can be controlled within the limits of about 1,000 to4,000.

Under otherwise identical reaction conditions, the molecular weight ofthe reaction products increases as the amount of catalyst and/or theamount of formaldehyde are increased.

Preferably the condensation reaction is carried out in the presence of asolvent. Particularly suitable solvents are aliphatic, aromatic orcycloaliphatic hydrocarbons having boiling points between about 70° and150° C. Particularly contemplated solvents include the following:Benzene, toluene and a mixture of hydrogenated aliphatic hydrocarbons inthe boiling range from 140 to 170° C., called "Esso-Varsol".

If the reaction is carried out at 70° C, it is completed after about 4hours and at 100° C it is completed after as little as 15 minutes.Generally speaking, the reaction is conducted at a temperature between50° and 150° C, preferably between 70° and 100° C for between 15° and240 minutes.

The products are prepared with the use of different solvents and whilemaintaining various temperatures and reaction periods do not differ intheir physical properties. For example, when using4,4'-thio-bis-(3-methyl-6-t-butylphenol) as the starting bisphenol, thehydroxyl numbers of the 4,4'-thio-bis-(dialkylphenol)/formaldehydecondensates range between 289 and 305.

The following general structures can be derived herefrom for thelow-molecular units: ##STR4## In these formulas, the substituents R₁, R₂and R'₁ and R'₂ have the meaning mentioned above. The bridge linksbetween the thio-bis-phenol units are methylene or dimethylene ethergroups. The presence of both groups could be detected in the IRspectrum.

The compounds which are obtainable by the process according to theinvention are outstanding antioxidants for plastic materials. Polymersof various constitutions, e.g., polyolefins, are subject to seriousdeterioration by thermal autoxidation and oxidative photodegradation.Degradation by oxidation occurs especially at higher temperatures andresults in embrittlement and crazing or cracking at the surface of thematerial. The degradation of polymers is counteracted by the use ofantioxidants among which 4,4'-thio-bis-(3-methyl-6-t-butylphenol) hasfound particularly wide application. For several applications of thisbisphenol, its relatively high vapor pressure is disadvantageous. It hasthe result that, as elevated temperatures such as those which may occurduring processing of the material mixed with the bisphenol, all or partof the stabilizer is evaporated so that its protective action is lost orreduced. Additionally, the migrated or exuded stabilizer may deposit inthe processing machines resulting in troubles in the processing andfabricating procedure.

As disclosed in U.S. Pat. No. 3,247,262, less volatile antioxidants canbe prepared by oxidative coupling of monophenols containingunsubstituted hydrogen atoms in ortho or para position with respect tothe phenolic hydroxyl group with cupric salts of organic acids. However,due to the low molecular weight of the starting phenols, the compoundsobtained show only slightly improved vapor pressure properties.

According to German Offenlegungsschrift No. 1,793,192 compounds havinghigher molecular weights are obtained by oxidative coupling ofsulfur-containing bisphenols which contain unsubstituted hydrogen ino-position. This process furnishes products having molecular weightswhich do not exceed about 1,000 and containing less than 75% of thephenolic hydroxy groups contained in the starting compounds.

While the stability in processing of plastic materials in which thesecompounds are incorporated as antioxidants is somewhat improved, it isnot sufficient in all cases. This behavior is probably due to thereaction in the number of hydroxy groups as compared with that of thestarting compounds.

In addition to the higher molecular weight, the products prepared by thenew process differ from the substances obtained by oxidative couplingadvantageously by the fact that the phenolic hydroxy groups arepreserved and the ratio of bridge sulfur atoms to phenolic hydroxygroups is not altered. This ratio is of particular importance for theactivity as antioxidant. The novel compounds are useful as antioxidantsfor any plastic materials and are preferably used for stabilizingpolyolefins, especially polyethylene. Additionally, they may be used toprevent cross linking which, for example, has very disadvantageousconsequences in film production and, due to inhomogeneities, may resultin rupture of the extruded film. They are usually incorporated in theplastic materials in amounts of 0.01 to 1.0% by weight based on theweight of the polymer.

The products according to the invention can be used not only alone asdifficultly migrating antioxidants but also in combination with furtherstabilizers, lubricants and antiblocking agents, UV absorbers and otheradditives. The production of the novel compounds and their use asstabilizers are illustrated by the following examples.

In order to more fully illustrate the nature of the invention and themanner of practicing the same the following examples are presented:

EXAMPLE 1

Into a four-necked flask equipped with a Teflon stirrer, refluxcondenser, thermometer and dropping funnel and having a capacity of 2liters were charged 500 ml benzene which was heated at 80° C to mildboiling. Then 179 g 4,4'-thio-bis-(3-methyl-6-t-butylphenol) weredissolved in the benzene. To this solution was added through thedropping funnel within 30 minutes a mixture of 37.5 g of a 32% formalinsolution, 29.0 g of 32% hydrochloric acid and 1.8 g oxalic acid. Theoxalic acid served to brighten the condensates, its presence being notabsolutely necessary.

The reaction mixture was refluxed for about 4 to 5 hours at 72° to 75° Cwhile vigorously stirring. Upon completion of the reaction, thehydrochloric acid was removed in the same reaction vessel by washingseveral times with distilled water. The lower phase containinghydrochloric acid can be conveniently drained through a drain valveattached to the bottom. Thereafter the solvent was evaporated undervacuum. 181 grams of a faintly yellowish resin having a molecular weightof 1030 and a hydroxyl number of 350 remained as the residue.

EXAMPLE 2

By the procedure of Example 1, 179 g4,4'-thio-bis-(3-methyl-6-t-butylphenol) and 37.5 g of a 32% formalinsolution were reacted under the same reaction conditions but with 58.0 gof a 32% hydrochloric acid. After processing, 185 g of a yellow coloredresin having a molecular weight of 1590 and a hydroxyl number of 301were obtained.

EXAMPLE 3

Following the procedure of Example 1, 179 g of4,4'-thio-bis-(3-methyl-6-t-butylphenol) and 37.5 g of a 32% formalinsolution were reacted with 29.0 g of 32% hydrochloric acid. Deviatingfrom the apparatus described in Example 1, a separator forazeotropically separating the water produced in the reaction wasinserted between the reflux condenser and reaction vessel. After 4 hoursof reaction, 55 ml water had separated. After usual processing andevaporation of the solvent, 182 g of a yellow brown colored resin havinga molecular weight of 2,030 and a hydroxyl number of 298 were obtained.

EXAMPLE 4

179 grams 4,4'-thio-bis-(3-methyl-6-t-butylphenol) were reacted underthe conditions of Example 1 with the same amounts of a formaldehydeexcept that 500 ml of a mixture of aliphatic hydrocarbons boiling at150° C were used as the solvent in place of benzene. Due to the higherreaction temperature of 100° C, the reaction began immediately and theformaldehyde was reacted already after 30 minutes. After processing, ayellow brown colored resin having a molecular weight of 1,240 and ahydroxyl number of 284 was obtained.

EXAMPLE 5

The efficiency of the novel compounds as stabilizers was determined asfollows: The melt viscosity (MFI 190/5 according to DIN 53 735) ofpolyethylene having a molecular weight of about 80,000 and havingincorporated the condensation product of4,4'-thio-bis-(3-methyl-6-t-butylphenol) and formaldehyde was measured.An electrically heated Zwick capillary plastometer 4104 was used for themeasurements. 4 grams of granules containing 0.0875% stabilizer wereintroduced into the test cylinder. After a fusion period of 4 minutes,the piston having been inserted was loaded with a 5 kgs weight. After aninitial travel of the piston for 1 minute, the first i₅ value wasdetermined. Thereafter, one waited (about 20 to 30 minutes dependingupon the i₅ value) until the remainder of the test specimen was extrudedthrough the orifice under the same load. After having cleaned thepiston, the test cylinder and the orifice, the extruded test specimenhaving been cut into pieces of 3 cm. length was introduced again and thenext measurement made in the manner described above. This procedure waseffected five times on the same test specimen. The test temperature was240° C.

In the graph attached hereto, the dependence of the melt viscosity (MFI190/5) on the number of extrusions in the capillary plastometer isrepresented.

As is obvious from the diagrammatic representation, substantialimprovements have been obtained as compared with the control product4,4'-thio-bis-(3-methyl-6-t-butylphenol) 1 and the condensation product2 of German Offenlegungsschrift No. 1,793,192. Already the meltviscosities of the starting granules are higher for the condensationproducts 3 and 4 according to the invention than for the controlstabilizers 1 and 2. This fact suggests a lower degree of cross linkingof the polyethylene powder charged during granulation. Moreover, thereduction in melt viscosity found when extruding the test specimenrepeatedly in the capillary plastometer (ΔMFI 190/5) is markedly lowerthan that of the control stabilizers. This favorable behavior of thestabilizers according to the invention can be attributed to theincreased molecular weight and the substantially lower migration rateattented therewith.

What is claimed is:
 1. A 4,4'-thio-bis-(dialkylphenol)/formaldehydecondensation product having a molecular weight of 1,000 to 4,000.
 2. Aphenol/formaldehyde condensation product having a repeating unit of theformula ##STR5## wherein n is 3 to 12, R₁ and R'₁ are each independentlyselected from the group consisting of straight chained alkyl of 1-8carbon atoms, branched chained alkyl of 1-8 carbon atoms, R₂ and R'₂ areeach independently hydrogen, straight chained alkyl of 1-8 carbon atoms,and branched chained alkyl of 1-8 carbon atoms.
 3. A phenol/formaldehydecondensation product having a repeating unit of the formula ##STR6##wherein n is 3 to 12, R₁ and R'₁ are each independently selected fromthe group consisting of straight chained alkyl of 1-8 carbon atoms,branched chained alkyl of 1-8 carbon atoms, R₂ and R'₂ are eachindependently hydrogen, straight chained alkyl of 1-8 carbon atoms orbranched chained alkyl of 1-8 carbon atoms.
 4. A phenol/formaldehydecondensation product according to claim 2 having a molecular weight of1,000 to 4,000.
 5. A phenol/formaldehyde condensation product accordingto claim 3 having a molecular weight of 1,000 to 4,000.
 6. A process forpreparing a condensation product of 4,4'-thio-bis-(dialkylphenol) andformaldehyde which comprises contacting a 4,4'-thio-bis-(dialkylphenol)having a free hydrogen atom in the ortho position with respect to eachphenolic hydroxyl group and a source of formaldehyde in the presence ofa protonic acid catalyst, the mol ratio of said4,4'-thio-bis-(dialkylphenol) to formaldehyde being 1:0.5 to 10 and themol ratio of said 4,4'-thio-bis-(dialkylphenol) to said protonic acidbeing 1:0.01 to
 10. 7. In a process for preparing a phenol/formaldehydecondensation process wherein a source of formaldehyde is condensed witha bisphenol in the presence of a protonic acid catalyst, the improvementwhich comprises employing as said bisphenol a compound of the formula##STR7## wherein R₁ and R'₁ are independently branched chained alkylgroups having up to 8 carbon atoms and R₂ and R'₂ are hydrogen, straightchained alkyl of 1 to 8 carbon atoms or branched chained alkyl having 1to 8 carbon atoms, the mol ratio of said 4,4'-thio-bis-(dialkylphenol)to said formaldehyde being 1:0.5 to 10 and the mol ratio of said4,4'-thio-bis-(dialkylphenol) to protonic acid being 1:0.01 to
 10. 8. Aprocess according to claim 6 wherein the 4,4'-thio-bis-(dialkylphenol)is 4,4'-thio-bis-(3-methyl-6-t-butylphenol) and the source offormaldehyde is formaldehyde.
 9. A process according to claim 8 when theformaldehyde is present in the form of an aqueous solution.
 10. Aprocess according to claim 6 wherein the mole ratio of4,4'-thio-bis-(dialkylphenol) to formaldehyde is 1:0.8 to 3.0.
 11. Aprocess according to claim 6 wherein the condensation is carried out inan aliphatic, cycloaliphatic or aromatic hydrocarbon having a boilingpoint of 80° to 150° C in which said 4,4'-thio-bis-(dialkylphenol) andsaid source of formaldehyde are soluble.
 12. A process according toclaim 6 wherein said protonic acid catalyst is selected from the groupconsisting of hydrochloric acid, phosphoric acid, p-toluene sulfonicacid, a mixture of hydrochloric and oxalic acid, a mixture ofhydrochloric and sulfuric acid and a mixture of hydrochloric and boricacid.
 13. A process according to claim 11 wherein said solvent isbenzene.